As is well known, silicone rubber is useful particularly in the medical field as a result of its inert nature and compatibility with human tissue. However, for a number of reasons, silicone elastomers per se display drawbacks in various medical and other utilities. In addition to expense, in the instance of catheters, silicone rubber per se is soft limp and thus difficult to insert into human tissues. However, the inert nature of silicone elastomers with regard to tissue, drugs, etc. strongly recommends use as catheters and other such medical uses.
Silicone rubber is also employed as closures for bottles or containers adapted to receive a needle through the closure to draw, for instance, injectable materials. However, the silicone rubber tends to "core" as the needle is passed therethrough, and is not heat sealable thereby precluding bonding of the closure to the container as is desirable particularly with sterilized materials. Clearly a "core" which may be inadvertently injected is of substantial concern.
Accordingly, the instant invention addresses the inert nature of silicone elastomers and provided a heretofore unavailable method of bonding such elastomers to polyolefin materials, i.e. polyethylene and polypropylene, having cost and properties very useful in the medical field. Polypropylene is particularly advantageous in that when bonded the composite can be autoclaved.
For instance, by bonding an outer film of silicone rubber to polypropylene tubing, a catheter primarily of low cost polyolefin having desirable rigid or stiffened structure for insertion into tissue is produced in a straight forward, economical fashion. By enclosing a silicone closure body within a polyolefin film, the closure may be hermetically bonded by, for instance, induction or ultrasonic welding, of the polyolefin to the container. The outer polyolefin film surface tends to preclude "coring" of the closure as the needle is passed therethrough thereby avoiding the inadvertent deposit of closure material into the contents of the closure or in the needle. As will be described in more detail below, a polyolefin surface film strengthens the silicone material at the interface between the materials. A needle may be passed through the composite material with a substantially reduced chance of removing a "core".